Conventionally, there is known a parking area system that aims at enabling effective use of a parking area provided together with a shop. The parking area system is configured so that, when a vehicle approaches a facility (e.g., parking area or shop), an in-vehicle device transmits a user ID, which is used for identifying a user, to a facility-side device. When the facility-side device confirms the user ID, the facility-side device transmits information associated with the user to the in-vehicle device. For example, the information associated with a user includes information to provide leading customers with special parking spaces, special benefit information, and information from shops that meet preferences of users extracted from the Internet usage history (e.g., see patent literature 1). In the description below, these kinds of information will be referred to as assistance information because the information is useful to users (that is, the information supports users).
The prior-art parking area system may allow the in-vehicle device to transmit a user ID to an invalid access point (hereinafter referred to as an “unauthorized access point”) in response to a transmission request from the unauthorized access point. The user ID also provides, to the unauthorized access point, information capable of specifying behavior of the user or the vehicle. The information may be abused by a third party that installed the unauthorized access point.